Online sensor calibration for electrohydraulic valves

ABSTRACT

An online method for reconfiguring pressure and position sensors in a hydraulic system is disclosed. In one step, a sensor drift condition, a recalibration request, or an unisolated fault condition is detected. In another step, a system pressure sensor or another sensor, such as a load-sense pressure sensor, is verified as a trusted master reference sensor. Another step includes measuring and recording a first pressure reading at the master reference sensor and first voltage readings associated with first, second, third, and fourth pressure slave sensors at a first pump pressure set point. Another step includes, repeating the previous step at a second pump pressure set point. A new gain and offset for each of the first, second, third, and fourth pressure sensors can be calculated based on a comparison of the recoded first and second pressure readings and the recorded first and second voltage readings.

RELATED APPLICATIONS

This application is a divisional of application Ser. No. 14/105,532,filed Dec. 13, 2013, which application claims priority to provisionalapplication Ser. No. 61/745,965, filed Dec. 26, 2012 and claims priorityto provisional application Ser. No. 61/737,612, filed Dec. 14, 2012,which applications are incorporated herein by reference in theirentirety.

BACKGROUND

Work machines, such as fork lifts, wheel loaders, track loaders,excavators, backhoes, bull dozers, and telehandlers are known. Workmachines can be used to move material, such as pallets, dirt, and/ordebris. The work machines typically include a work implement (e.g., afork) connected to the work machine. The work implements attached to thework machines are typically powered by a hydraulic system. The hydraulicsystem can include a hydraulic pump that is powered by a prime mover,such as a diesel engine. Work machines are commonly provided withelectronic control systems that rely upon a number of inputs andoutputs, for example, pressure sensors, position sensors, and valveactuators. In such electro-hydraulic systems, the added reliance on suchcomponents has led to the increased prevalence of system faults,including sensor drift. These systems rely on the accuracy of thesensors to achieve accurate flow control and other system functions andcontrol performance can be compromised when the sensors are inaccurate.It is known to recalibrate sensors by removing them from the system andconnecting them to a test stand, but this is often not feasible, and isnot available on demand or in an online environment in an active workmachine. Improvements in sensor recalibration methods are desired.

SUMMARY

An online method for reconfiguring pressure sensors in a hydraulicsystem is disclosed. In one embodiment, the hydraulic system isassociated with a work machine. The hydraulic system may include anelectro-hydraulic system having a control system, a system pump, asystem pressure sensor, a load-sense pressure sensor, a first valvehaving a first pressure sensor in fluid communication with a head sideor a first side of a first actuator, a second valve having a secondpressure sensor in fluid communication with a rod side or second side ofthe first actuator, a third valve having a third pressure sensor influid communication with a head side or a first side of a secondactuator, and a fourth valve having a fourth pressure sensor in fluidcommunication with the rod side or second side of the second actuator.Examples of the first and second actuators are linear actuators andhydraulic motors. In one step, one of a sensor drift condition, arecalibration request, and an unisolated fault condition is detected. Inanother step, the pressure sensor or the load-sense pressure sensor isverified as a trusted master reference sensor. Another step includesmeasuring and recording a first pressure reading at the system pressuresensor and first voltage readings associated with the first, second,third, and fourth pressure sensors at a first pump pressure set point.Another step includes, measuring and recording a second pressure readingat the system pressure sensor and second voltage readings associatedwith the first, second, third, and fourth pressure sensors at a secondpump pressure set point. In one step a new gain and offset for each ofthe first, second, third, and fourth pressure sensors is calculatedbased on a comparison of the recoded first and second pressure readingsand the recorded first and second voltage readings.

The step of verifying that the pressure sensor or the load-sensepressure sensor can be trusted as a master reference sensor can includesetting the pump to a predetermined pressure and then commanding thefirst and third valves to open to the system pump and recordingpressures sensed at the system, first, and third pressure sensors. Afterthe first and third valves are closed, another step can be commandingthe second and fourth valves to open to the system pump and recordingpressures sensed at the system, second, and fourth pressure sensors.Another step includes analyzing the recorded pressures againstpredefined condition data stored in the control system.

DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments are described with referenceto the following figures, which are not necessarily drawn to scale,wherein like reference numerals refer to like parts throughout thevarious views unless otherwise specified.

FIG. 1 is a schematic view of a control architecture having featuresthat are examples of aspects in accordance with the principles of thepresent disclosure.

FIG. 2 is a perspective view of a work machine for which the controlarchitecture of FIG. 1 may be used.

FIG. 3 is a schematic of a hydraulic system and electronic controlsystem that may be associated with the work machine of FIG. 2.

FIG. 4 is a process flow chart showing a procedure in which a pressuresensor in the system shown in FIG. 3 is established as a referencesensor in a fault isolation procedure.

FIG. 5 is a table showing possible analytical results and correspondingactions resulting from the procedure shown in FIG. 4.

FIG. 6 is a continuation of the table shown in FIG. 6.

FIG. 7 is a process flow chart showing a procedure in which the pressuresensors can be recalibrated online.

FIG. 8 is a process flow chart showing a procedure in which the positionsensors can be recalibrated online.

DETAILED DESCRIPTION

Various embodiments will be described in detail with reference to thedrawings, wherein like reference numerals represent like parts andassemblies throughout the several views. Reference to variousembodiments does not limit the scope of the claims attached hereto.Additionally, any examples set forth in this specification are notintended to be limiting and merely set forth some of the many possibleembodiments for the appended claims.

General Architecture Overview

The present disclosure relates generally to fault isolation schemes foruse in hydraulic actuation systems. In certain embodiments, a controlsystem architecture is used that is modularized and distributed. Byusing a modularized approach, the system can be reduced in complexityand can provide enhanced flexibility. By using a distributedarchitecture with overlapping and redundant fault detection strategies,fault isolation is enhanced. The controllers included in the systeminclude a process and a non-transient storage medium or memory, such asRAM, flash drive or a hard drive. The memory is for storing executablecode, the operating parameters, and the input from the operatorinterface while the processor is for executing the code.

FIG. 1 illustrates an example fault detection, isolation andreconfiguration (FDIR) architecture 20 in accordance with the principlesof the present disclosure. The FDIR architecture 20 is adapted toprovide control of a hydraulic actuation system of a vehicle such as aconstruction vehicle. In one example embodiment, the FDIR architecture20 can be used to control a hydraulic actuation system of a wheel loader22 (see FIG. 2). The FDIR architecture 20 includes a supervisorycontroller 24 adapted to interface with a main controller 26 of thewheel loader 22. The supervisory controller 24 is at a supervisorycontrol level of the hydraulic actuation system. For example, thesupervisory controller 24 supervises and interfaces with a plurality ofcontrol nodes (e.g. control modules, control subsystems, etc.) that areat a node level of the FDIR architecture 20. The FDIR architecture 20 isconfigured such that all of the nodes report back through thesupervisory controller 24. In certain embodiments, there is no directcross communication between the nodes. Instead, the nodes interfacevertically with the supervisory controller 24, which functions tocoordinate operation of the various nodes. As shown at FIG. 1, the nodescan include a pump control node 28, a tilt cylinder control node 30, alift cylinder control node 32, a boom suspension system control node 34,a tank control unit node 36 and one or more additional auxiliary nodes38.

Example Vehicle for Application of Recalibration Procedure

FIG. 2 illustrates a wheel loader 22, which is an example of a type ofconstruction vehicle to which aspects of the present disclosure can beapplied. The wheel loader includes a chassis or frame 52 supported onwheels 54. A cab 56 is supported on the frame 52. A boom 58 is pivotallyconnected to the frame 52. A lift cylinder 60 is used to pivot the boom58 upwardly and downwardly relative to the frame 52. A bucket 62 ispivotally mounted at the end of the boom 58. A tilt cylinder 64 is usedto pivot the bucket 62 relative to the boom 58.

Example Architecture Schematic

FIG. 3 illustrates a schematic of system architecture suitable for usein controlling the hydraulic actuation system of the wheel loader 22.The architecture includes the supervisory controller 24 that interfaceswith the pump control node 28, the tilt cylinder control node 30, thelift cylinder control node 32, the boom suspension system control node34 and the tank control unit node 36 (auxiliary nodes are not shown).The pump control node 28 controls the hydraulic fluid pressure and flowrate needed to satisfy the flow and pressure requirements of the tiltcylinder control node 30, the lift cylinder control node 32 and the boomsuspension system control node 34. The tank control unit node 36receives the hydraulic fluid flow discharged from the tilt cylindercontrol node 30, the lift cylinder control node 32 and the boomsuspension system control node 34. The tilt cylinder control node 30controls the hydraulic fluid flow provided to and from the tilt cylinder64 of the wheel loader 22. The lift cylinder control node 32 controlsthe hydraulic fluid flow provided to and from the lift cylinder 60 ofthe wheel loader 22. The boom suspension system control node 34 controlsthe hydraulic fluid flow provided to and from an accumulator 66. Theboom suspension system control node 34 also controls fluid communicationbetween the accumulator 66 and the lift cylinder 60.

The tilt cylinder control node 30 is in fluid communication with the oneor more pumps of the pump control node 28 and functions to selectivelyplace a head side 74 or a rod side 76 of the tilt cylinder 64 and fluidcommunication with the pump or pumps. Similarly, the tilt cylindercontrol node 30 is in fluid communication with the system tank 77 (i.e.,the system reservoir) through the tank control unit node 36 andfunctions to selectively place the head side 74 or rod side 76 of thetilt cylinder 64 and fluid communication with the tank 77.

The tilt cylinder control module 30 includes a head side flow controlvalve Vth that selectively places the head side 74 of the tilt cylinder64 in fluid communication with either the system pump/pumps or thesystem tank. The tilt cylinder control node 30 also includes a rod sideflow control valve Vtr that selectively places the rod side 76 of thetilt cylinder 64 in fluid communication with either the systempump/pumps or the system tank. Valve position sensors Xth and Xtr areprovided for respectively sensing the spool positions (i.e., the sensorsdetect positions of valve spools within valve sleeves, such as LVDT typesensors) of the head side flow control valve Vth and the rod side flowcontrol valve Vtr. Additionally, pressure sensors Pth and Ptr areprovided for respectively sensing the head side and rod side pressuresof the tilt cylinder 64. In one embodiment, the pressure sensors in thesystem are strain-based pressure sensors. The tilt cylinder control node30 also includes a component controller Ct that controls operation ofthe valves Vth, Vtr based on commands (e.g., mode, pressure or spoolposition demands, etc.) received from a supervisory controller 24 andfeedback provided by the sensors of the node. The component controllerCt also monitors the node for failure conditions and reports anydetected failure conditions to the supervisory controller 24 as raisedfault flags.

The lift cylinder control node 32 is in fluid communication with one ormore pumps of the pump control node 28 and functions to selectivelyplace the one or more pumps in fluid communication with a head side 70or a rod side 72 of the lift cylinder 60. Similarly, the lift cylindercontrol node 32 is in fluid communication with the tank 77 through thetank control unit node 36 and is configured to selectively place thehead side 70 and the rod side 72 of the boom cylinder 60 in fluidcommunication with the tank 77.

The lift cylinder control node 32 includes a head side flow controlvalve Vlh and a rod side flow control valve Vlr. The head side flowcontrol valve Vlh is configured to selectively place the head side 70 ofthe boom cylinder 60 in fluid communication with either the one or morepumps of the pump control node 28 or the system tank 77. The rod sideflow control valve Vlr is configured to selectively place a rod side 72of the boom cylinder 60 in fluid communication with either one of thesystem pumps or the system tank 77. The lift cylinder control mode 32further includes a head side valve position sensor Xlh for sensing aspool position of the head side valve Vlh and a rod side valve positionsensor Xlr for sensing the spool position of the rod side flow controlvalve Vlr. In one embodiment, Xlh and Xlr are LVDT type positionsensors. The lift cylinder control node 32 also includes a pressuresensor Plh2 for sensing the pressure of the head side 70 of the boomcylinder 60, and a pressure sensor Plr for sensing the hydraulicpressure at the rod side 72 of the boom cylinder 60. The lift cylindercontrol node 32 further includes a component level controller Cl thatinterfaces with the various sensors of the lift cylinder control node32. The component controller Cl also interfaces with the supervisorycontroller 24. The component controller Cl controls the operation of thevalves Vlh, Vlr based on demand signals (e.g., mode, pressure, spoolposition demands, etc.) sent to the component controller Cl by thesupervisory controller 24 and based on feedback provided by the sensorsof the lift cylinder control node 32. The component controller Ll alsomonitors the fault conditions that may arise within the lift cylindercontrol node 32 and reports such fault conditions to the supervisorycontroller 24 as raised fault flags.

The boom suspension system control node 34 is in fluid communicationwith the one or more pumps of the pump control node 28 and is configuredto selectively place an accumulator 66 in fluid communication with theone or more pumps to charge the accumulator 66. The boom suspensionsystem control node 34 can also place the accumulator 66 in fluidcommunication with the tank 77 and/or the head side 70 of the liftcylinder 60.

The boom suspension system control node 34 includes a charge valve Vcand a damping valve Vd. The charge valve Vc can be used to charge theaccumulator 66 by placing the accumulator 66 in fluid communication witha pump of the pump control node 28. The damping valve Vd is used toselectively place the accumulator 66 in fluid communication with a headside 70 of the boom cylinder 60. The boom suspension system control node34 further includes a charge valve position sensor Xc that senses thespool position of the charge valve Vc. The boom suspension systemcontrol node 34 also includes a damping valve position sensor Xd thatsenses a position of the damping valve Vd. The boom suspension systemcontrol node 34 further includes a pressure sensor Pa that senses apressure of the accumulator 66, and a pressure sensor Plh1 that sensesthe pressure at the head side 70 of the boom cylinder 60. The sensors ofthe boom suspension system control node 34 interface with a nodecontroller Cbss which provides node level control of the boom suspensionsystem control node 34. The controller Cbss interfaces with thesupervisory controller 24 and reports fault conditions within the nodeto the supervisory controller 24 as raised fault flags. The controllersends operational commands (e.g., mode, pressure, spool positiondemands, etc.) to the valves.

The optional tank control unit node 36 includes a tank flow controlvalve Vt that controls system flow to the system tank 77. The tankcontrol unit node 36 also includes a pressure sensor Pt that senses thepressure of the system tank 77 at a location upstream from the valve Vt.A position sensor Xt senses a position of the valve Vt. A componentcontroller Ct is provided for controlling operation of the valve Vt. Thecomponent controller Ct interfaces with the sensors of the mode and alsointerfaces with the supervisory controller 24. Operation of the valve Vtis controlled by the component controller Ct based on commands (e.g.,mode, pressure, spool position demands, etc.) received from thesupervisory controller 24 and feedback from the node sensors. Thecomponent controller Ct monitors operation of the node and reports anyfailure conditions to the supervisory controller 24.

Establish Reference Pressure Sensor Procedure

Referring to FIG. 4, a procedure 1000 is initiated in which a masterreference pressure sensor is established for use in the recalibrationprocedure 1100 of FIG. 7. Procedure 1000 may also be used to establish amaster pressure sensor for use in an isolation procedure as well. It isnoted that although the figures diagrammatically show steps in aparticular order, the described procedures are not necessarily intendedto be limited to being performed in the shown order. Rather at leastsome of the shown steps may be performed in an overlapping manner, in adifferent order and/or simultaneously.

In a first step 1002 of the method 1000, the electronic controller 50detects that one or more sensors have drifted. In addition oralternatively, the electronic controller 50 receives a request torecalibrate the sensors. In another circumstance, an un-isolated faultis detected somewhere within the controller(s), the work circuit, oranother related system associated with work machine 22. Because manyelectro-hydraulic systems may contain complex algorithms dependent upona large number of sensors and inputs, a fault condition is frequentlyidentified before the actual fault is isolated. As such, step 1002 canreflect the initial condition where it is known that a fault hasoccurred, but it is not known what component(s) are actually responsiblefor triggering the fault. Accordingly, the recalibration process 1100,discussed later, can be used after method 1000 is completed as a firstapproach to resolving the fault without having to resort to an off-linefault isolation process and/or a stand-alone process to recalibrate thesensors after unacceptable sensor drift has been detected.

At step 1004, while the system is still on-line, each of the tilt andlift valves (Vth, Vtr, Vlh, Vlr) are sequentially opened to the tank 77with the tank valve Vt, where provided, in the open position. For eachvalve, the associated pressure at the valve and the system pressure arerecorded. Optionally, a predetermined delay after opening the valve totank may be implemented before recording the pressure. Once thepressures are recorded, the valve is commanded to the closed or neutralposition and the next valve is opened to the tank.

As an example illustration of step 1004, the following order could beused after valve Vt, where provided, is opened: (1) command valve Vth toopen to the tank 77, sense and record the pressure at Pth and Ps after apredetermined delay, command valve Vth to the closed position; (2)command valve Vtr to open to the tank 77, sense and record the pressureat Ptr and Ps after a predetermined delay, command valve Vtr to theclosed position; (1) command valve Vlh to open to the tank 77, sense andrecord the pressure at Plh2 and Ps after a predetermined delay, commandvalve Vlh to the closed position; (2) command valve Vlr to open to thetank 77, sense and record the pressure at Plr and Ps after apredetermined delay, command valve Vlr to the closed position. Oneskilled in the art will understand, upon learning the concepts presentedherein, that other valve orders are possible.

At step 1006, the pump 29 of the pump control node 28 responsible forproviding fluid pressure to the hydraulic circuit is commanded to apredetermined pressure set point. Where the pressure sensor Ps indicatesthat the system pressure equals the predetermined pressure, theprocedure moves to step 1008. Where the system pressure does not equalthe predetermined pressure set point, a further evaluation may benecessary. In the signal from sensor Ps is unstable and below theminimum calibration pressure, a fault within the pump control node 28may exist. Where the signal from sensor Ps is stable and above theminimum calibration pressure, a number of potential faults may exists,for example an pump control node fault, a hydraulic short, and/or asteering demand fault.

In either case, where pump 29 is unable to meet the pressure set point,the system will command the pump 29 to full stroke or maximum output atstep 1010 where the pump pressure at Ps is calibrated against thepressure compensator associated with the pump 29. Where it is determinedthat Ps equals the maximum pressure of the compensator, then theprocedure is allowed to proceed to step 1008. Where the pressure at Psis not equal to the expected maximum compensator pressure, the proceduremoves to step 1022 where a fault in the pump control node 28 must beisolated and/or recalibrated. If, after step 1022 is completed andfurther faults exist, the procedure may be reinitiated at step 1006where the proper operation of the pump 29 and node 28 can be verifiedbefore proceeding to step 1008.

At step 1008, the head side valves Vth, Vlh of the tilt and liftactuators 60, 64 are commanded to open to the pump 29. Once opened, andafter an optional time delay, the pressures at the Pth; Plh2; and Ps arerecorded. Subsequently, valves Vth, Vlh are opened to the tank and thenplaced in the closed position after an optional time delay. By onlyopening valves on one side of each actuator 60, 64 it can be betterassured that no movement of a load occurs. It is also noted that thewhile actuators 60, 64 are shown as being linear actuators, they mayalso be hydraulic motors.

At step 1012, the rod side valves Vtr, Vlr of the tilt and liftactuators 60, 64 are commanded to open to the pump 29. Once opened, andafter an optional time delay, the pressures at the Ptr; Plr; and Ps arerecorded. Subsequently, valves Vth, Vlh are opened to the tank and thenplaced in the closed position after an optional time delay.

At step 1014, the recorded data is analyzed to determine if Ps, oranother sensor, can be used as a trusted reference sensor forrecalibration. Four outcomes are shown as being possible from theanalysis: (1) Ps can be trusted and will be used as a referencesensor—outcome 1016; (2) Ps cannot be trusted, but Pls+margin can betrusted and will be used as a reference sensor—outcome 1018; (3) arecalibration can be implemented, after which the procedure returns backto step 1006 to determine if Ps can be trusted—outcome 1020; or there isan apparent fault in the pump control node 28 which must be isolated orcorrected—outcome 1022.

Referring to FIGS. 5-6, a decision chart 1014 a, 1014 b (hereafterreferred to collectively as chart 1014) is shown that can be used inanalysis step 1014 to determine which of outcomes 1016-1022 result. Inthe analysis step 1014, Ps is initially compared to readings from theother pressure sensors. The decision chart, as disclosed, includescondition data that utilizes different threshold values for thesereading differences. For example, a fault condition will be identifiedif the difference is more than a first threshold, for example 6 bar. Acalibration condition can be identified if the difference is more than asecond threshold, but less than the first threshold, for example, thedifference is between 2 bar and 6 bar. Where the difference is less thanthe second threshold value, then the difference is small enough to nottrigger either a fault condition or a calibration condition. It shouldbe understood that more or fewer threshold conditions could be utilizedand that different numerical values may be used for the threshold valuesin analysis step 1014 without departing from the concepts herein.

Referring to chart 1014, an action is described for each possible dataanalysis result based on the number and combination of fault andcalibration conditions identified. It is noted that the particular casesdescribed in the paragraphs below are directed to a system with fourvalves (Vth, Vtr, Vlh, Vlr) with pressure sensors (Pth, Ptr, Plh2, Plr),a system pressure sensor (Ps), and a load sense pressure sensor (Pls).The decision chart 1014 can be modified as necessary to account forother cases that would arise from other system configurations.

Case 1 is an analysis result where no faults are identified relative toPs. In this case, Ps can be taken to be trusted and used as a reference,and outcome 1016 results.

Case 2 is an analysis result where only one fault is identified relativeto Ps. In this case, it is still acceptable to use Ps as a trustedreference, and outcome 1016 results. It is noted that any subsequentrecalibration or isolation procedure can be configured to start with anevaluation of the sensor associated with the fault condition.

Case 3 is an analysis result where two faults relative to Ps areidentified in the same service, meaning that two faults are identifiedthat are both either associated with lift actuator 60 or tilt actuator64. In this case, it is still acceptable to use Ps as a trustedreference, and outcome 1016 results. It is noted that any subsequentrecalibration or isolation procedure will start with an evaluation ofthe sensors associated with the fault condition.

Case 4 is an analysis result where two faults relative to Ps areidentified in different services. Where Ps is equal to Pls plus apredetermined margin (i.e. Pls+margin), then it is acceptable to use Psas a trusted reference, and outcome 1016 results. However, where this isnot the case, then the pump control node 28 must be isolated orcorrected under outcome 1022 before any further steps can be taken.

Case 5 is an analysis result where three faults relative to Ps areidentified. If the three faulted sensors agree with Pls+margin, wherethe margin is estimated from the average of the three faulted sensors,then outcome 1018 results and Pls+margin can be trusted and used for therecalibration. However, where this is not the case, then the pumpcontrol node 28 must be isolated or corrected under outcome 1022 beforeany further steps can be taken.

Case 6 is an analysis result where four faults relative to Ps areidentified, meaning that none of the pressure sensors agree with Ps. Ifthe four faulted sensors agree with Pls+margin, where the margin isestimated from the average of the three faulted sensors, then outcome1018 results and Pls+margin can be trusted and used for therecalibration. However, where this is not the case, then the pumpcontrol node 28 must be isolated or corrected under outcome 1022 beforeany further steps can be taken. If the standard deviation of the fourfaulted sensors is clustered, then a fault likely exists with the Ps orPls sensors.

Case 7 is an analysis result where one fault condition and twocalibration conditions relative to Ps are identified. In this instance,outcome 1020 results and a recalibration of Ps can be implemented, afterwhich the procedure returns back to step 1006 to determine if Ps can betrusted, but with the system at a different pressure. The recalibrationof Ps can be performed with reference to the two calibrations and theone good sensor and/or with reference to a master reference sensor.

Case 8 is an analysis result where one fault condition and threecalibration conditions relative to Ps are identified. In this instance,outcome 1020 results and a recalibration of Ps can be implemented, afterwhich the procedure returns back to step 1006 to determine if Ps can betrusted, but with the system at a different pressure. The recalibrationof Ps can be performed with reference to the three calibrations and/orwith reference to a master reference sensor.

Case 9 is an analysis result where one fault condition and onecalibration condition are identified relative to Ps in the same service,meaning that two faults are identified that are both either associatedwith lift actuator 60 or tilt actuator 64. In this case, it is stillacceptable to use Ps as a trusted reference, and outcome 1016 results.It is noted that any subsequent recalibration or isolation procedure canbe configured to start with an evaluation of the sensor associated withthe fault condition.

Case 10 is an analysis result where once fault condition and onecalibration condition relative to Ps are identified in differentservices. Where Ps is equal to Pls plus a predetermined margin (i.e.Pls+margin), then it is acceptable to use Ps as a trusted reference, andoutcome 1016 results. However, where this is not the case, then the pumpcontrol node 28 must be isolated or corrected under outcome 1022 beforeany further steps can be taken.

Case 11 is an analysis result where two fault conditions on the sameservice and one calibration condition relative to Ps are identified. Inthis instance, outcome 1020 results and a recalibration of Ps can beimplemented, after which the procedure returns back to step 1006 todetermine if Ps can be trusted, but with the system at a differentpressure. The recalibration of Ps can be performed with reference to theone calibration condition sensor and/or with reference to a masterreference sensor.

Case 12 is an analysis result where two fault conditions on a differentservice and one calibration condition relative to Ps are identified. Inthis instance, outcome 1020 results and a recalibration of Ps can beimplemented, after which the procedure returns back to step 1006 todetermine if Ps can be trusted, but with the system at a differentpressure. The recalibration of Ps can be performed with reference to theone calibration condition sensor and the one good sensor and/or withreference to a master reference sensor.

Case 13 is an analysis result where two fault conditions and twocalibration conditions relative to Ps are identified. If the fourfaulted/calibration sensors agree with Pls+margin, where the margin isestimated from the average of the four faulted/calibration sensors, thenoutcome 1018 results and Pls+margin can be trusted and used for therecalibration. However, where this is not the case, then the pumpcontrol node 28 must be isolated or corrected under outcome 1022 beforeany further steps can be taken. If the standard deviation of the fourfaulted/calibration sensors is clustered, then a fault likely existswith the Ps or Pls sensors.

Case 14 is an analysis result where three fault conditions and onecalibration condition relative to Ps are identified. If the threefaulted sensors agree with Pls+margin, where the margin is estimatedfrom the average of the three faulted sensors, then outcome 1018 resultsand Pls+margin can be trusted and used for the recalibration. However,where this is not the case, then the pump control node 28 must beisolated or corrected under outcome 1022 before any further steps can betaken.

Case 15 is an analysis result where three calibration conditionsrelative to Ps are identified. In this instance, outcome 1020 resultsand a recalibration of Ps can be implemented, after which the procedurereturns back to step 1006 to determine if Ps can be trusted, but withthe system at a different pressure. The recalibration of Ps can beperformed with reference to the lift head side sensor reading, to thenearest calibration condition sensor, and/or to a selected masterreference sensor.

Case 16 is an analysis result where four calibration conditions relativeto Ps are identified. In this instance, outcome 1020 results and arecalibration of Ps can be implemented, after which the procedurereturns back to step 1006 to determine if Ps can be trusted, but withthe system at a different pressure. The recalibration of Ps can beperformed with reference to the lift head side sensor reading, to thenearest calibration condition sensor, and/or to a selected masterreference sensor.

Case 17 is an analysis result where one calibration condition relativeto Ps is identified. In this instance, the recalibration can becontinued under outcome 1016 or the calibration condition sensor can berecalibrated relative to Ps under outcome 1020. Where it is chosen torecalibrate the calibration condition sensor, the procedure returns backto step 1006 after recalibration to determine if Ps can be trusted, butwith the system at a different pressure.

Case 18 is an analysis result where two calibration conditions relativeto Ps in the same service are identified. In this instance, outcome 1020can result and a recalibration of the two calibration condition sensorscan be implemented, after which the procedure returns back to step 1006to determine if Ps can be trusted, but with the system at a differentpressure. The recalibration of the two calibration condition sensors canbe with reference to Ps. Alternatively, the recalibration can becontinued under outcome 1016 without recalibrating the two sensorsassociated with the calibration conditions.

Case 19 is an analysis result where two calibration conditions relativeto Ps in a different service are identified. In this instance, outcome1020 can result and a recalibration of the two calibration conditionsensors can be implemented, after which the procedure returns back tostep 1006 to determine if Ps can be trusted, but with the system at adifferent pressure. The recalibration of the two calibration conditionsensors can be with reference to Ps. Alternatively, the recalibrationcan be continued under outcome 1016 without recalibrating the twosensors associated with the calibration conditions.

It is to be understood that the above described cases are exemplary innature and that other case conditions and corresponding actions may bechosen without departing from the concepts presented herein.

Online Pressure Sensor Recalibration

Once a reference sensor has been established, the online sensorrecalibration process 1100 may be implemented, as shown at FIG. 7. It isnoted that although two three-way valves are shown for the tilt and liftactuators, one four-way valve could be used instead wherein one four-wayvalve is associated with each actuator. Also, four two-way valves couldbe used. In such a case the function of Vth and Vtr would be embodied ina single valve as would the function of Vlh and Vlr. One skilled in theart, upon learning of the disclosure of this application, willunderstand that processes 1000 and 1100 can also be performed witheither two-way valves, four-way valves, another type of valve, andcombinations thereof without departing from the concepts presentedherein. Furthermore, processes 1000 and 1100 can be applied to systemshaving more than tilt and lift actuator functions.

In a first step 1102 of the process, a master sensor and slave sensorsare established. Where the above described protocol for establishing areference sensor has been utilized, the master sensor is the trustedreference sensor and the slave sensors are the remaining sensors.

In a step 1104, each of the tilt and lift valves (Vth, Vtr, Vlh, Vlr)are opened to the tank 77 with the tank valve Vt, where provided, in theopen position. After a delay, the valves are commanded to the closed orneutral position and the next valve is opened to the tank.

At step 1106, the pump 29 of the pump control node 28 responsible forproviding fluid pressure to the hydraulic circuit is commanded to afirst predetermined pressure set point, for example 25 bar.

At step 1108, the head side valves Vth, Vlh of the tilt and liftactuators 60, 64 are commanded to open to the pump 29. Once opened, andafter an optional time delay, the master pressure (e.g. Ps) is recorded,as are the slave sensor voltages (e.g. Pth, Plh2). Subsequently, valvesVth, Vlh are opened to the tank and then placed in the closed positionafter an optional time delay. By only opening valves on one side of eachactuator 60, 64 it can be better assured that no movement of a loadoccurs. However, it should be understood that this results when usingtwo valves per actuator and not necessarily when using a single four-wayvalve for each actuator.

At step 1110, the rod side valves Vtr, Vlr of the tilt and liftactuators 60, 64 are commanded to open to the pump 29. Once opened, themaster pressure (e.g. Ps) is recorded, as are the slave sensor voltages(e.g. Ptr, Plr). Subsequently, valves Vtr, Vlr are opened to the tankand then placed in the closed position after an optional time delay.

At step 1112, the pump 29 of the pump control node 28 responsible forproviding fluid pressure to the hydraulic circuit is commanded to asecond predetermined pressure set point, for example 200 bar.

At step 1114, the head side valves Vth, Vlh of the tilt and liftactuators 60, 64 are commanded to open to the pump 29. Once opened, andafter an optional time delay, the master pressure (e.g. Ps) is recorded,as are the slave sensor voltages (e.g. Pth, Plh2). Subsequently, valvesVth, Vlh are opened to the tank and then placed in the closed positionafter an optional time delay. By only opening valves on one side of eachactuator 60, 64 it can be better assured that no movement of a loadoccurs.

At step 1116, the rod side valves Vtr, Vlr of the tilt and liftactuators 60, 64 are commanded to open to the pump 29. Once opened, themaster pressure (e.g. Ps) is recorded, as are the slave sensor voltages(e.g. Ptr, Plr). Subsequently, valves Vtr, Vlr are opened to the tankand then placed in the closed position after an optional time delay.

Once the above information has been acquired, a new gain and offset foreach slave sensor can be computed using known methods under step 1118.Optionally, the new gain and offset can be verified at a step 1120 whichmay include repeating steps 1112 to 1116 at a different, third pressure.If it is determined that the new gain and offset are correct and/orshould be used under step 1122, the recalibration mode can then beexited at step 1126. If it is determined that the new gain and offsetare incorrect a calibration error can be indicated at step 1124 and therecalibration mode can be exited under step 1126.

Online Position Sensor Recalibration

The position sensors Xth, Xtr, Xlh, Xlr associated with the lift andtilt valves can also be recalibrated online by using end stop readingsand stored end stop values. With reference to FIG. 8, a position sensorrecalibration process 1200 is shown. In a step 1202, the valves arecommanded sequentially or simultaneously to a first end stop and theposition or voltage from the corresponding position sensor is recorded.In a step 1204, the valves are commanded sequentially or simultaneouslyto a second opposite end stop and the position or voltage from thecorresponding position sensor is recorded. In a step 1206, in caseswhere the valve center position can be trusted to remain constant, thevalves are commanded to a center position, and the position voltage fromthe corresponding position sensor is also recorded. It is noted thateach of steps 1202, 1204, and 1206 can be performed in conjunction withthe online pressure sensor recalibration process 1100 since the samevalves will be placed in the desired position for position sensorrecalibration during process 1100.

Once the above information has been acquired, a new gain and offset foreach slave sensor (e.g.) can be computed using known methods under step1208. Optionally, the new gain and offset can be verified at a step 1210which may include repeating steps 1202 to 1206 with the new gain andoffset. If it is determined that the new gain and offset are correctand/or should be used under step 1212, the recalibration mode can thenbe exited at step 1216. If it is determined that the new gain and offsetare incorrect a calibration error can be indicated at step 1214 and therecalibration mode can be exited under step 1216.

In order to enhance the accuracy of the recalibration process 1200, thehydraulic fluid temperature at which the stored end stop values wererecorded can be taken into account during step 1208. Likewise, accuracyis increased if the recalibration of the position sensors can beperformed at a temperature that is within an acceptable range of thetemperature present when the end stop positions were stored. Also, wherethe valve center position can be trusted to remain constant, athree-point calibration is possible using step 1206. Where a two-pointcalibration is used, a linear adjustment to the existing calibration canbe used.

The various embodiments described above are provided by way ofillustration only and should not be construed to limit the claimsattached hereto. Those skilled in the art will readily recognize variousmodifications and changes that may be made without following the exampleembodiments and applications illustrated and described herein, andwithout departing from the true spirit and scope of the disclosure.

What is claimed is:
 1. An online method for reconfiguring positionsensors in a hydraulic system comprising the steps of: (a) commanding aplurality of valves in the hydraulic system to move to a first end stopposition and recording position sensor first voltages corresponding tothe plurality of valves; (b) commanding the plurality of valves in thehydraulic system to move to a second end stop position and recordingposition sensor second voltages corresponding to the plurality ofvalves; (c) computing a new gain and offset for each of the plurality ofposition sensors based on a comparison of the recoded end stop first andsecond voltages with respect to stored end stop position data; and (d)recalibrating the position sensors with the new gain and offset for eachposition sensor.